A liquid crystal display (LCD) includes an LCD panel formed with liquid crystal cells and pixel elements with each associating with a corresponding liquid crystal cell. These pixel elements are substantially arranged in the form of a matrix having gate lines in rows and data lines in columns. The LCD panel is driven by a driving circuit including a gate driver and a data driver. The gate driver generates a plurality of gate signals (scanning signals) sequentially applied to the gate lines for sequentially turning on the pixel elements row-by-row. The data driver generates a plurality of source signals (data signals), i.e., sequentially sampling image signals, simultaneously applied to the data lines in conjunction with the gate signals applied to the gate lines for aligning states of the liquid crystal cells on the LCD panel to control light transmittance therethrough, thereby displaying an image on the LCD.
In such a driving circuit, a bi-directional shift register is usually utilized in the gate driver to generate the plurality of gate signals for sequentially driving the gate lines, so as to allow a positive or a reverse display image. Typically, a plurality of 2-to-2 bi-directional control circuits is employed in the bi-directional shift register to control the scanning direction, forward or backward, of the plurality of gate signals.
FIG. 7 illustrates a conventional 2-to-2 bi-directional control circuit having two input terminals P and N, and two output terminals D1 and D2, and is operably controlled by two control signals Bi and XBi. The control signals Bi and XBi are two DC signals set to have opposite polarities, such as a high level voltage and a low level voltage, and used to set the 2-to 2 bi-directional control circuits in a manner to direct input signals in the shift register to be shifted in a forward or backward direction. However, the use of the 2-to 2 bi-directional control circuit in each stage of the shift register may cause voltage drops in input signals of the stage, and increase power consumption and manufacture costs.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.